1. Field of the Invention
The invention is directed to the use of N-polyhydroxyalkyl fatty acid amides as thickening agents for liquid aqueous surfactant systems.
2. Discussion of the Background
The volume of production of liquid products in the cosmetics and detergents sector is continually increasing. In recent years the following products have particularly increased in importance: liquid shampoos, bubble baths, and shower preparations, i.e. liquid soaps for use in dispensers which deliver soap to the hand. Liquid dish washing detergents and liquid fine fabric detergents have also acquired substantial markets.
Any useful liquid surfactant formulation must meet the requirement of good shelf life. The liquid should not become turbid or produce sedimentation when subjected to temperature fluctuations. The product should have minimum tendency to have a defatting action on skin, and should not irritate skin.
A liquid surfactant system should have a viscosity which is suited to the intended application, and should be variable over as wide a range as possible.
Thus, viscosity is an important criterion for the quality of a liquid surfactant preparation. For example, for a douche gel one requires a very high viscosity, whereas for a shampoo one ordinarily desires a relatively liquid behavior with relatively low viscosity (1000-4000 mPa-sec).
Known thickeners for liquid surfactant formulations include, among others, nonionic fatty acid polyalkylene glycol esters, such as Antil.RTM. (molecular weight about 3000; provided by the firm Goldschmidt AG), as well as nonionic fatty acid alkanolamides, which have been used for many years (see 1958 J. Am. Oil Chemists' Soc., 35, 548). The preferred fatty acid alkanolamide is coconut oil fatty acid diethanolamide (Superamide.RTM.), which has thickening properties which are superior to those of other fatty acid diethanolamides.
The degree of thickening depends strongly on the surfactant system and on the electrolytes added. Thus, for example, it is known that when secondary paraffin-sulfonates are employed as surfactants in liquid preparations, problems are presented in adjusting the viscosity. The known commercially available thickeners mentioned above have insufficient thickening action in systems with secondary paraffinsulfonates in the presence of electrolytes. Viscosity adjusting problems also occur when surfactant mixtures containing paraffinsulfonates are employed as often recommended, e.g. paraffinsulfonate with ether sulfate. See 1976, Fette--Seifen--Anstrichmittel, 78, 200.